When last ______ valuable, those books enjoyed great success.
| A．finding | B．found | C．being found | D．to be found |
They were surprised that a child could work out the problem ______ they themselves couldn’t.
| A．once | B．while | C．then | D．If |
--- I hear Jane has gone to the Holy Island for her holiday.
--- Oh, how nice! Do you know when she ______ ?
| A．was leaving | B．had left | C．has left | D．Left |
The factory was built in a secret place, around _____ were high mountains.
| A．where | B．it | C．that | D．Which |
The teachers were discussing the research project that they would like to see _____ in the coming holiday.
| A．complete | B．completes | C．completing | D．to complete |
--- It’s the office! So you ______ know smoking is not allowed here.
--- Oh, sorry.
| A．must | B．will | C．may | D．Need |